cl_drawhud
cl_drawhud is a console variable available in all 
Source games.
Using the cl_drawhud cvar is very easy and is very useful for developers looking to take professional images of their work in-game. Disabling cl_drawhud will remove the health, armor, and ammo indicators from your screen so you only have the weapon remaining (which can also be removed).
Note:The HUD is only visible when cl_drawhud is set to 1.